1. Field of the Invention
The present invention relates to a resist film removing method for removing from a substrate a resist film having a surface cured by a process, such as an ion implantation process or etching process. The present invention also relates to a computer readable storage medium that stores a control program for executing a method of this kind.
2. Description of the Related Art
In manufacturing semiconductor devices, ion implantation techniques are utilized to implant predetermined ions into a semiconductor wafer made of a silicon substrate, and various films, such as an insulating film, disposed on the surface of a silicon substrate, so as to change their surface property. For example, a p-n junction can be formed in a substrate by implanting ions of, e.g., arsenic (As), phosphorous (P), and/or boron (B) into the substrate.
In general, an ion implantation process is performed after a resist film having a predetermined circuit pattern is formed on a substrate (which means an underlying material present under the resist film, such as a silicon substrate or one of various films disposed on the surface of the silicon substrate or the like). The resist film is removed after the ion implantation process. In this respect, where the resist film is used for ion implantation of a high concentration, a less-strippable cured layer is formed on the surface of the resist film, so it becomes difficult to peel off the resist film from the substrate. Accordingly, in general, where a resist film with a cured layer formed at the surface is removed, a method is adopted such that a plasma ashing process is first performed on the resist film, and a wet cleaning is then performed on the substrate (for example, Jpn. Pat. Appln. KOKAI Publication No. 7-37780).
However, the substrate may be damaged due to the plasma ashing process performed on the resist film. For example, the substrate may be oxidized by implanted ions, the ashing gas may be introduced into the substrate to change its property due to anisotropy of the plasma ashing, or an electric discharge may be caused from the substrate charged with electricity by the plasma ashing.
Further, when the plasma ashing process is performed on the resist film, the resist film is heated and generates gases from the inside, such as gasified solvent components and/or nitrogen gas (N2). Consequently, a phenomenon, so-called popping, occurs such that the gases break the cured layer of the resist film and spurt therefrom, thereby blowing out the resist film. This popping occurs because the temperature of a heating process performed subsequently to the resist film development process is lower than the temperature of the plasma ashing process performed thereafter. In this case, a non-cured state (a state having viscosity), which is substantially unchanged between before and after an ion implantation process, is present inside the resist film, in which a component that can be vaporized by heat applied during the plasma ashing process is remaining. If popping occurs, droplets of the non-cured part may be scattered from the exploded resist film and deposited on the substrate. If the droplets are deposited on the substrate, it is difficult to remove them by wet cleaning of the substrate.
In order to solve the problem described above, the following approach has been adopted in place of the plasma ashing process (for example, Jpn. Pat. Appln. KOKAI Publication No. 2001-93806). Specifically, water is supplied onto a resist film while a substrate therebelow is heated to generate cracks in a cured layer of the resist film. In this case, the water is allowed to permeate through the cracks into the resist film up to the boundary between the resist film and substrate. Consequently, the resist film is peeled off from the substrate, or set to be easily peeled off from the substrate.
However, in the case of the technique according to Jpn. Pat. Appln. KOKAI Publication No. 2001-93806, it is necessary to generate a lot of cracks in the cured layer of the resist film, so as to effectively remove the resist film. If the heating temperature is set higher for this purpose, the resist film may cause popping, thereby allowing droplets of a non-cured part to be scattered onto the substrate. Accordingly, this technique is tolerant of crack generation only to the extent that does not entail popping of the resist film, resulting in difficulty in sufficiently removing the resist film.